Linear phosphonitrilic chloride (LPNC) has been used as a catalyst to equilibrate organopolysiloxanes. Other LPNC-type materials, such as Cl.sub.2 PONPCl.sub.3 "PONP" , have also been found to be effective as catalysts. These materials, hereinafter collectively designated "phosphorus-nitrogen chloride" (PNC), have been made by procedures involving the use of PCl.sub.5 and an ammonium salt, as disclosed in U.S. Pat. No. 3,839,388.
U.S. Pat. No. 3,835,388 discloses the use of vacuum in combination with a phosphonitrilic halide as an equilibration catalyst to facilitate the condensation and/or equilibration of silanol fluids. This process deals with the synthesis of the catalytic linear phosphonitrilic chloride (LPNC) species. This process utilizes toxic solvents, expensive separation techniques, and long reaction times. Such process drawbacks limit the production, and subsequent use of such catalysts in industry.
Preparation of LPNC catalysts has been disclosed by Emsley et al. in J. Chem. Soc. (A), 3025 (1970). This process uses phosphorus pentachloride and ammonium chloride as starting materials in solvents such as nitrobenzene. The reaction is carried out at elevated temperatures (&gt;130.degree. C.) and requires separation techniques for handling the air sensitive solids. Similarly, U.S. Pat. No. 5,210,129 uses phosphorus pentachloride and ammonium chloride as starting materials for the synthesis of LPNC catalysts. The reaction temperatures vary between 100.degree. C. and 220.degree. C., and the preferred reaction time is in excess of 6 hours.
The processes used for the synthesis of LPNC catalysts use undesirable toxic solvents, have longer reaction times, and need temperatures well in excess of 100.degree. C. Such requirements make it difficult to make LPNC catalysts on larger scales and hamper their ease of use. There is thus a need for a process to make a LPNC catalyst that can be easily handled and used. It is desirable to have such procedures avoid the use of toxic solvents or cumbersome techniques. The process needs to be convenient such that the LPNC thus synthesized could be easily used as a catalyst without lengthy isolation procedures.
It has been surprisingly found that the process of the present invention can be carried out without using undesirable solvents such as nitrobenzene or tetrachloroethane. The process yields LPNC in a siloxane medium, which is preferred for storage and use because of compatibility with the utility of LPNC as an organosiloxane catalyst.